APL Instrument Sheds Light on the Moon's Darkest Mysteries

APL is playing an important role in NASA’s Lunar Reconnaissance Orbiter (LRO) mission by operating the Miniature-Radio Frequency (Mini-RF) radar instrument—and making a major contribution toward new understanding of the Moon’s surface features and composition.

More than 3 years ago, NASA tapped APL for the final integration and testing of two Mini-RF instruments—synthetic aperture radar devices that would fly on separate spacecraft and, among other activities, scan permanently shadowed lunar craters for traces of ice. Laboratory scientists and engineers delivered, not just preparing the instruments for launch, but applying critical APL technical and scientific capabilities to make Mini-RF a powerful part of NASA’s most productive lunar mission in decades.

Eight months after the first Mini-RF flew on India’s Chandrayaan-1 mission, its more advanced “twin” was one of seven instruments launched on LRO in June 2009. LRO results came quickly, among them indications that permanently shadowed regions might harbor water and hydrogen. This finding included analysis of data from Mini-RF, produced by the instrument’s ability to peer into the dark polar craters that cannot be seen from Earth.

As the mission progressed, the APL team developed a process that allowed Mini-RF to collect much more data than originally planned. Mini-RF operators crafted ways to take advantage of spare downlink capacity in the mission schedule without tapping additional spacecraft resources. The radar could scan the Moon’s night side, for example, where devices that need visible light typically do not operate.

In the Mini-RF operations center on the APL campus, planning and commanding of Mini-RF is conducted by scientists using the APL-developed “SciBox” tool. Once data are collected and returned to Earth through a ground station at White Sands, New Mexico, they are sent to APL and processed into radar images and other science products.

Original mission plans called for Mini-RF to gather two 6- by 240-mile “strips” of data per month; the instrument has since collected more than a thousand strips of data covering about two-thirds of the lunar surface, including 95% of both polar regions. Instead of the planned 2 hours of science collection, Mini-RF has actually gathered more than 400 hours of science data. By March 2011, the LRO mission will have processed and released more data to the scientific community than all previous planetary missions combined. This includes more than 38 terabytes of Mini-RF data—more than three times the printed collection of the Library of Congress. These data are sent to NASA’s Planetary Data System archive, where they are made available to all lunar researchers.

Mini-RF has proven that a small, lightweight synthetic aperture radar instrument can be part of a larger payload, instead of requiring a dedicated spacecraft (as needed on past radar missions, such as Magellan). Meeting another mission goal, the Mini-RF antenna was demonstrated as a spacecraft uplink and downlink communications system, able to transmit and receive modulated signals from Earth—a technology that could allow future missions to save mass and power. Backed by 50 years of APL space experience—which includes building and operating more than 150 space instruments—Mini-RF represents a key part of this important lunar expedition.